The present invention relates to a device for mounting and accurately seating a perforating or cutoff blade along a cylinder such as might be used for partially or completely severing a web at a plurality of locations along its length. Such devices are particularly useful in machines for continuous printing or collating of paper webs.
One of the requirements for such blade mounting arrangements is that the cutting edge of a perforating blade be capable of accurate seating against an anvil surface. Otherwise, an uneven perforation will result, with some sections of the perforation being too deep, or some sections being too shallow, or both. This produces variation in the tear strength along the perforation, with resultant high probability of jamming in subsequent printers or bursters. A backup or anvil cylinder may be included for providing a hardened anvil surface, or insert, or in some cases a die, to cooperate with the sharpened edge of the properly seated blade in perforating the passing web as the web moves between the rotating blade cylinder and anvil or backup cylinder.
The blade is mounted to the rotating cylinder by clamping the blade into a recess or slot cut generally lengthwise into the cylinder periphery. The blade may be clamped against one of the side faces of the recess, or against an intermediate supporting bar. Several techniques are available, however, for providing proper seating of the cutting edge of the blade against the anvil surface.
Typically, when a perforating blade is manufactured, it includes some variation in height from its base to its cutting edge, as well as a tendency to bow in a vertical direction. One method for seating the blade is to use a blade which has been manufactured to very close tolerances with respect to both height and bow. The cylinder is provided with a recess that has been machined also to very close tolerances with respect to a uniform and specific depth. Seating of the blade is relatively simple, since the blade is loaded into the recess, with the base of the blade bottomed along the base of the recess, and is then clamped tightly in place.
Despite the simplicity of the seating process, this technique possesses several readily apparent disadvantages. By requiring very close tolerances in manufacturing of the blades, the cost of the blades is increased significantly. Similarly, the cost of the cylinder into which the recess is cut is also increased, particularly in view of the fact that such cylinders typically have as many as eight such recesses for mounting up to eight blades at one time. Moreover, in the event that blade height or recess depth varies even slightly from blade to blade or recess to recess, the cutting edge of a blade extending slightly further from the recess than another will be dulled relatively quickly through contact with the anvil surface.
A second technique is available, in which a blade having very loose height and bow tolerance may be used. The blade is inserted into the recess, but is not bottomed against the base of the recess, and is secured somewhat loosely along its length. The blade is then seated against the anvil surface, through a procedure known as "crash in". This procedure consists of rotating the blade cylinder and anvil cyliinder, with or without a web passing therebetween, at inching speed through one revolution. The cutting edge of the blade is free to move under the seating force sufficiently into the recess, at whatever locations are necessary to obtain a uniform seating of the cutting edge against the anvil. While secured somewhat loosely, the blade must be nonetheless held tight enough to hold its seated position. The apparatus is then stopped and the blade is securely clamped along its entire length to prevent slip within the recess when the apparatus is operated at higher speeds.
While this technique requires a more complicated blade seating technique, it allows the use of blades and cylinders manufactured to much looser tolerances, with substantial cost savings. A third technique, possessing some of the advantages and disadvantages of both techniques, utilizes a blade having close tolerance with respect to height only. While the blade is bottomed against the recess base, crash in is required to remove vertical bow from the blade.
It will be noted that the foregoing discussion is equally applicable in the case of cuttoff blades.
A number of various devices for accurately securing a blade within a recess, suitable for holding the blade both for crash in and for clamping, are known. For instance, the blade may be placed against a side wall of the recess, and a bar inserted into the recess adjacent the blade. A plurality of bolt members are threaded into holes in the bar, extending from the side of the bar to the recess side wall opposite the blade. To clamp the blade, the bolt members are driven in a direction outwardly from the bar against the recess wall. Driving of the bolt members forces the bar tightly against the blade, thereby clamping it in place. In using such a device, the bolt members may be partially tightened, allowing the blade limited movement for seating against the anvil surface during crash in, and then the bolt members may be completely tightened for clamping.
Several disadvantages are present in such a blade holding device. In order to provide relatively uniform clamping force on the blade, a relatively large number of the bolt members must be provided disposed along the length of the bar. Thus, the clamping operation becomes a time-consuming process. Furthermore, positioning of the bolt members for crash in must be fairly precise, since there is a relatively narrow force range suitable for crash in wherein the blade is held loosely enough for movement during seating but tight enough to retain the seated position. Furthermore, the bolt members also must be finally tightened to a relatively uniform degree, or uneven perforation will result where the blade is inadequately clamped. Consequently, during crash in and in clamping the blade, either a torque wrench must be used, or the operator must through experience develop a "feel" for the proper tightening of the bolt members.
In U.S. Pat. No. 2,832,411, issued Apr. 29, 1958, to Richards et al, another blade holding device is disclosed, for use in conjunction with a cylinder having a recess that is at an angle with respect to the axis of the cylinder. A pair of wedge bars, each extending for substantially the full length of the recess, are located within the recess with the blade inserted between the bars. The ends of the cylinder are provided with collars, each having a slot adjacent the recess, into which a bolt is fitted. The bolts each have a pair of flanges near the head, and when the bolts are placed into the slots, the flanges fit one on each side of the slot. Each bolt extends into a threaded bore in an end of one of the wedge bars, such that by rotating the bolts, each bar may be moved in either direction along the cylinder recess. To clamp the blade, the bolts are rotated such that the wedge bars are driven into the recess so as to wedge the blade into place. Notches or other indicia are provided along the upper surface of one of the wedge bars and the cylinder surface, so that the relative movement of the bar in relation to the cylinder for aligning the blade may be easily determined.
The Richards et al device reduces the number of bolts which must be manipulated during the clamping process in comparison with the single-bar device described above. It does not, however, address the problem of holding the blade for seating during crash in, and in fact, shows the blade bottomed on the recess base. Moreover, the Richards device possesses several disadvantages that make it impractical, particularly for use with a blade that must be seated for uniform perforation.
Because the force exerted upon the blade must be substantially uniform to ensure uniform perforation, the fit of the wedge bars into the recess must be very precise. Thus, very close tolerances must be provided in the widths of the wedge bars, recess, and blade, since variations in these dimensions will produce variations in the "tightness" of the fit of the wedge bars within the recess as the bars are wedged into place, thereby producing variations in the force applied to blade. As a result, not only is manufacture of the bars, recess and blade made difficult and expensive, but the slightest mishandling of these parts during use may be sufficient to misalign them to the extent that uniform force is no longer attainable.
Further, since the range of force values acceptable for crash in is relatively narrow, careful positioning of the bars is required prior to crash in. This requires the expenditure of significant amounts of time, use of special tools, and/or the development of special skills by the operator for proper adjustment of the bars.
What is needed, therefore, is a blade holding device for use with a cylinder in which the blade may be clamped in a relatively quick and simple manner. Such a device should require manipulation of few parts during the clamping operation, and should not require the use of any special tools or special skills on the part of the operator. The device should enable the blade to be secured loosely into the cylinder with uniform securing force, properly seated against an anvil surface, and then tightly clamped into place. Clamping force should be uniformly applied along the length of the blade. The device should be relatively simple to manufacture, and should not require unreasonably tight manufacturing tolerances.